1. Field of the Invention
The invention relates to a tamper-evident adhesive security tape or label which has an optically active security feature and an optical feature.
An optically active feature for the present purposes comprehends diffractive structures, diffraction gratings, surface reliefs, holograms, kinegrams, and the like.
2. Description of the Related Art
Adhesive security tapes or labels in the sense of the present invention fulfill two functions: on the one hand, the adhesive tape or label is intended to ensure the authenticity of a product or the integrity of a pack through the provision of an optically active security feature. Preference for this purpose is given to the use of holograms, which are well established in the product protection segment and therefore offer a high degree of acceptance, recognizability, and security. On the other hand, however, an attempt at tampering, in other words an unauthorized attempt to detach the adhesive tape or label, is to be clearly recognizable. The latter measure ensures that the user can be reasonably certain that a product protected with an adhesive tape or label of this kind is genuine and in its original packaging.
Typical holograms which are already being used today in product protection and as security features for documents of value customarily have a basic metallically lustrous appearance which gives rise, on a change in the viewing angle, to a play of rainbow colors as a result of diffraction of light at the structures of the hologram. These diffractive effects, however, are always very similar, and the metallic luster is common to all such products. Consequently there is a demand for new optically variable effects which differ from the conventional effect not only in the pattern of the hologram but also in the basic color and/or by virtue of a different luster.
Known from KR 10079525 is a hologram film and a method for its production. The construction there consists of a backing substrate, a release layer, an embossed layer (hologram layer), a partial metal layer, a masking layer, a print layer, and an adhesive layer. The print layer and the adhesive layer there have different fluorescent features. Evidence of tampering is not possible with this construction.
Known additionally, from decorative applications and packaging applications, are what are called dry peel labels. The feature of such labels is that the label consists of two parts which can be easily separated from one another. After the label has been adhered to an object, these two parts are initially still connected. When the upper part of the label, which often has a grip tab or the like, is then removed, the bottom part of the label remains, together with the self-adhesive coating, on the object. On the side facing away from the object, however, the self-adhesive coating is covered by a sheet or a varnish layer, and so the part that remains on the object no longer feels tacky (“dry”). Furthermore, as a result of this specific design, it is virtually impossible to adhere again the part of the label that has been removed, since the removed part as well is no longer tacky.
Combinations of such dry peel labels with a tamper-evident feature are also known, from EP-A 1 113 059, for example. The adhesive tape or label described therein, however, does not have any optically active security features.